Nofollow tags are a fairly recent invention. The history of nofollow goes something like this:
1. Google gives priority to sites with many links.
2. Spammers use blogs and guestbooks to artificially increase their link counts.
3. Somebody proposes that certain places on the web – like blogs and guestbooks – should have a way of devaluing any links that are added.
4. Search engines listened. Well, some of them. Well, Google.
Search Engine Journal did a recent posting: 13 reasons why nofollow tags suck. I couldn’t agree more!